Ferrule and ferrule with optical fiber

ABSTRACT

A ferrule of the present invention includes a positioning mechanism for positioning an optical fiber, and a recess having at least a first inner wall for allowing a front end of the optical fiber portion positioned by the positioning mechanism to protrude, and a second inner wall opposite to the first inner wall. A distance between the first inner wall and the second inner wall is less than or equal to four times the outer diameter of the optical fiber. Adhesive is filled into the recess and cured in a state in which the optical fiber protrudes from the first inner wall and substantially contacts the second inner wall to fix the optical fiber.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application ofSer. No. 12/878,502, filed on Sep. 9, 2010, whose priority is claimed onJapanese Patent Application No. 2010-148288 filed on Jun. 29, 2010, thecontents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a ferrule mounted to a front end of anoptical fiber in order to optically connect the optical fiber with anoptical part, such as an optical element on a board or a module or anoptical fiber mounted on another connector and to a ferrule with anoptical fiber.

2. Description of the Related Art

In recent years, a scheme of fixing an optical fiber so that an opticalelement, such as a light emitting element (e.g., a semiconductor laser)or a light receiving element (e.g., a photo diode) mounted on a board isoptically connected with the optical fiber wired along the board andhaving an optical connector assembled with a front end thereof has beenwidely used.

When the optical fiber is optically connected with an optical element oranother optical fiber, deviation of an axial direction of the opticalfiber increases connection loss. Accordingly, it is necessary toposition an axis of the optical fiber in order to prevent the increaseof the connection loss.

For example, an optical path changing member having an optical-fiberinsertion hole into which an optical fiber is inserted, and a front-endarrangement space communicating with the optical fiber insertion hole isdescribed in Japanese Unexamined Patent Application, First PublicationNo. 2009-104096. In the optical path changing member, a front end of theoptical fiber is disposed in the front-end arrangement space, which isfilled with adhesive to fix the optical fiber to a predeterminedposition.

Thus, as in the case that an intermediate portion of the optical fiber(an optical fiber portion disposed in the insertion hole) is positionedand the front end of the optical fiber is disposed in the front-endarrangement space to adhere and fix the optical fiber, the adhesive isshrunk when cured, and thus force is applied to the optical fiber in thefront-end arrangement space in the lateral direction. As a result, thefront end portion of the optical fiber moves and an output directiondeviates. Even when a positioning mechanism for positioning the frontend of the optical fiber is formed in a ferrule in order to avoid such aproblem, it is necessary to precisely match positions of the positioningmechanism for positioning the front end portion and a positioningmechanism for positioning the intermediate portion, making it difficultto mold the ferrule.

The present invention has been achieved in view of the abovecircumstances, and it is an object of the present invention to provide aferrule capable of being easily molded and reducing a deviation of anoutput direction.

SUMMARY OF THE INVENTION

A ferrule according to an embodiment of the present invention is mountedto a front end of an optical fiber for optically connecting the opticalfiber to another optical part. The ferrule includes: a positioningmechanism for positioning an intermediate portion of the optical fiber;and a recess having at least a first inner wall for allowing the frontend of the optical fiber portion positioned by the positioning mechanismto protrude, and a second inner wall opposite to the first inner wall.The distance between the first inner wall and the second inner wall isless than or equal to four times the outer diameter of the opticalfiber. Adhesive is filled into the recess and cured in a state in whichthe optical fiber protrudes from the first inner wall and substantiallycontacts the second inner wall to fix the optical fiber.

The ferrule may be a resin that is transparent to a used wavelength.

The recess may have an adhesive application slot with an opening largerthan the distance between the first inner wall and the second innerwall.

The adhesive application slot may have an inclined surface at at leastone of the first inner wall and the second inner wall.

The ferrule may further include a reflecting portion for changing anoptical path between the front end of the optical fiber positioned bythe positioning mechanism and the other optical part.

In a ferrule with an optical fiber according to an embodiment of thepresent invention, the optical fiber is fixed to the ferrule.

An optical connector according to an embodiment of the present inventionincludes the ferrule.

A ferrule according to an embodiment of the present invention is aferrule for optically connecting an optical fiber to an optical part,and the ferrule includes a boot accommodating hole which is configuredto accommodate a boot attached to the optical fiber and which is formedon a rear end surface of the ferrule, an optical fiber hole which isconfigured to position an intermediate portion of the optical fiberhaving a predetermined outer diameter and which extends forward from afront end of the boot accommodating hole, and a recess configured for anadhesive to be disposed therein and comprising a first inner wall fromwhich a front end of the optical fiber positioned by the optical fiberhole is protrudable, and a second inner wall opposite to the first innerwall. The second inner wall is configured to be abutted by almost anentire area of a front end surface of the optical fiber, a bottom of therecess is positioned lower than a lower edge of the front end of theoptical fiber that protruded from the first inner wall, the recesscomprises an adhesive application slot with an opening larger than thedistance between the first inner wall and the second inner wall, thefirst inner wall comprising a first inclined surface, and the secondinner wall comprising a second inclined surface which does not reach afront face of the ferrule, and a distance between the first inner walland the second inner wall is more than or equal to half of the outerdiameter of the optical fiber and less than or equal to four times theouter diameter of the optical fiber.

In addition, the ferrule may be formed of a resin that is transparent toa wavelength of light transmitted through the optical fiber.

The ferrule may further comprises a reflecting portion reflecting lighton an optical path between the front end of the optical fiber positionedby the optical fiber hole and the optical part.

Moreover, an optical connector for optically connecting an optical fiberto an optical part according to an embodiment of the present inventionincludes an optical fiber and a ferrule. The ferrule includes a bootaccommodating hole which is configured to accommodate a boot attached tothe optical fiber and which is formed on a rear end surface of theferrule, an optical fiber hole which is configured to position at leastan intermediate portion of the optical fiber and which extends forwardfrom a front end of the boot accommodating hole, a recess comprising afirst inner wall from which a front end of the optical fiber protrudes,and a second inner wall opposite to the first inner wall, and anadhesive disposed in the recess and a surrounding portion of the opticalfiber protruding from the first inner wall. A bottom of the recess ispositioned lower than a lower edge of the front end of the optical fiberthat protruded from the first inner wall, the recess comprises anadhesive application slot with an opening larger than the distancebetween the first inner wall and the second inner wall, the first innerwall comprising a first inclined surface, and the second inner wallcomprising a second inclined surface which does not reach a front faceof the ferrule, a distance between the first inner wall and the secondinner wall is more than or equal to half of the outer diameter of theoptical fiber and less than or equal to four times the outer diameter ofthe optical fiber, and substantially an entire area of a front endsurface of the optical fiber abuts the second inner wall.

In the ferrule, a plurality of the optical fibers may be fixed, and thereflecting portion may include a recessed reflecting surface and may beprovided to each of the plurality of the optical fibers.

In the ferrule, a plurality of the reflecting portions may be arrangedin an arrangement direction of the plurality of the optical fibers.

In addition, the ferrule may include a lens located on an extension lineof the optical fiber.

Moreover, in the optical connector, the ferrule may include a lenslocated on an extension line of the optical fiber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view showing a ferrule with an optical fiber accordingto an embodiment of the present invention.

FIG. 1B is a cross-sectional view of the ferrule with an optical fibertaken along a line I-I of FIG. 1A according to the embodiment.

FIG. 2A is a plan view showing an example of a ferrule with an opticalfiber in a comparative example.

FIG. 2B is a cross-sectional view of the ferrule with an optical fibertaken along a line II-II of FIG. 2A in the comparative example.

FIG. 3 is a diagram for explaining position deviation of an opticalfiber due to shrinkage when adhesive is cured.

FIG. 4 is a plan view showing a ferrule according to another embodimentof the present invention.

FIG. 5A is a cross-sectional view of a ferrule taken along a line IV-IVof FIG. 4 in the embodiment.

FIG. 5B is a cross-sectional view of a ferrule taken along a line V-V ofFIG. 5A in the embodiment.

FIG. 6 is a cross-sectional view showing an example in which an opticalfiber is optically connected with an optical element on a board usingthe ferrule shown in FIG. 4.

FIG. 7A is a plan view showing a ferrule in which an adhesiveapplication slot with an inclined surface is formed in an embodiment.

FIG. 7B is a cross-sectional view of the ferrule taken along a lineVII-VII of FIG. 7A in the embodiment.

FIG. 8A is a plan view showing a ferrule with a convex lens in anembodiment.

FIG. 8B is a cross-sectional view of the ferrule taken along a lineVIII-VIII of FIG. 8A in the embodiment.

FIG. 9A is a plan view showing a ferrule with a recessed reflectingsurface in an embodiment.

FIG. 9B is a cross-sectional view of the ferrule taken along a lineIX-IX of FIG. 9A in the embodiment.

FIG. 10A is a cross-sectional view showing an example of an opticalfiber hole.

FIG. 10B is a cross-sectional view showing an example of a V-shapedgroove;

FIG. 10C is a cross-sectional view showing an example of a U-shapedgroove;

FIG. 11 is a cross-sectional view showing an example of a ferruleincluding a body with a V-shaped groove and a pressing lid.

FIG. 12A is a cross-sectional view showing an example of a state of anoptical connection using the ferrule in the example.

FIG. 12B is a cross-sectional view showing an example of a state of anoptical connection using the ferrule in the comparative example.

FIG. 13 is a graph showing an example of the result of measuring astandard deviation of a beam angle α according to the embodiment.

FIG. 14 is a perspective view showing a ferrule of a modified example.

FIG. 15 is a cross-sectional view partially showing the ferrule shown inFIG. 14 into which the inserted optical fiber is inserted.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the accompanying drawings.

As shown in FIGS. 1A and 1B, a ferrule 1 of the present embodiment ismounted to a front end of an optical fiber 2 and used to opticallyconnect the optical fiber 2 with another optical part. This ferrule 1has a positioning mechanism 7 for positioning an intermediate portion ofthe optical fiber 2, and a recess 6. This recess 6 has a first innerwall 6 b for allowing a front end portion of the optical fiber 2positioned by the positioning mechanism 7 to protrude, and a secondinner wall 6 a opposite to the first inner wall 6 b. In the ferrule 1,adhesive 4 is filled into the recess 6 and cured to fix the opticalfiber 2 in a state in which the optical fiber 2 protrudes from the firstinner wall 6 b and the front end of the optical fiber 2 substantiallycontacts the second inner wall 6 a.

This ferrule 1 may be used as a ferrule for an optical connector. Theoptical connector includes a ferrule 1, and a structure (e.g., ahousing, a latch, a screw, a spring, an arm, or an engagement pin) formechanically connecting the ferrule 1 to another optical part, or aboard or a module having the other optical part mounted thereon.

The optical fiber 2 is, for example, an optical fiber core wire, asingle-core optical fiber core wire led at a front end of a multi-coreoptical fiber tape core wire, an optical fiber strand, or a bare opticalfiber. In the example shown in FIG. 1B, an optical fiber 2 has a coating3 provided therearound. The coating 3 is removed (led) from the frontend portion of the optical fiber 2 disposed in the positioning mechanism7 and the recess 6. In this disclosure, the optical fiber portion whichis disposed in the positioning mechanism 7 and from which the coating 3has been removed is referred to as an intermediate portion of theoptical fiber 2. It is preferable that a front end face 2 a of theoptical fiber 2 is formed perpendicular to a longitudinal direction ofthe optical fiber 2.

The type of the optical fiber is not particularly limited, and may beany of a silica optical fiber, a plastic optical fiber, a multi-modeoptical fiber, a single-mode optical fiber or the like.

Examples of the positioning mechanism 7 for positioning the intermediateportion of the optical fiber 2 include an optical fiber hole 22 a shownin FIG. 10A, a V-shaped groove 22 b shown in FIG. 10B, and a U-shapedgroove 22 c shown in FIG. 10C. FIGS. 10A to 10C show cross-sectionalsurfaces perpendicular to the longitudinal directions of the positioningmechanism 7 and the optical fiber 12.

The ferrule 1 may be a single-core ferrule to which one optical fiber ismounted or a multi-core ferrule to which two or more optical fibers aremounted. The positioning mechanism 7 has an opening at the first innerwall 6 b so that the optical fiber 2 can protrude into the recess 6.When the optical fiber 2 is inserted into the positioning mechanism 7,gas such as air inside the positioning mechanism 7 is discharged intothe recess 6. This allows the optical fiber 2 to be smoothly insertedeven when a difference between an inner diameter of the optical fiberhole 22 a and an outer diameter of the optical fiber 2 is small.

In the present embodiment, the ferrule 1 includes a ferrule body 5integrally molded using a transparent material. The ferrule body 5 maybe formed of transparent resin, such as polycarbonate, modifiedpolyolefin, epoxy resin, and polyetherimide (PEI).

The ferrule body 5 may be manufactured, for example, using resin moldingsuch as injection molding. The shape of the ferrule body 5 is notparticularly limited. For example, the shape may be a flat cuboid or thelike.

To optically connect the optical fiber 2 disposed in the recess 6 toanother optical part, the second inner wall 6 a may be transparent to aused wavelength at least in an adjacent portion opposite to the frontend face 2 a of the optical fiber 2. In this case, other portions of theferrule body 5 may be formed of an opaque material. Further, light usedfor optical connection in the present invention is not limited tovisible light. The light may be ultraviolet light or infrared light. Thelight may be any light having small connection loss allowed for actualuse.

A reflective index of the material of the ferrule body 5 is notparticularly limited. The reflective index of the material may be higherthan, lower than, or equal to that of the optical fiber 2.

The recess 6 has an adhesive application slot 6 d with an upper opening.When the adhesive 4 is filled from the adhesive application slot 6 intothe recess 6 and cured, the optical fiber 2 is fixed to the recess 6 bythe adhesive 4. The adhesive 4 may penetrate into the positioningmechanism 7. Accordingly, even in the positioning mechanism 7, theintermediate portion of the optical fiber 2 may be fixed to the ferrule1.

It is preferable that the adhesive 4 is transparent to light and,particularly, has the same reflective index as the core of the opticalfiber 2. It is preferable that the adhesive 4 has an excellent adhesionforce with respect to the materials of the ferrule 1 and the opticalfiber 2 which are the adherends. Specifically, the adhesive 4 includesthermoset epoxy adhesive, acrylic adhesive, or the like.

It is preferable that, prior to filling and curing of the adhesive 4,the front end face 2 a of the optical fiber 2 contact (abut) the secondinner wall 6 a of the recess 6 in a state in which the front end face 2a of the optical fiber 2 is pressed into the second inner wall 6 a ofthe recess 6, so that there is no clearance between the front end face 2a of the optical fiber 2 and the second inner wall 6 a of the recess 6.When pressure is applied between the front end face 2 a of the opticalfiber 2 and the second inner wall 6 a, the front end portion of theoptical fiber 2 protruding from the first inner wall 6 b is more stablyheld in the recess 6. In this case, it is unnecessary for the opticalfiber 2 to contact a bottom portion 6 c of the recess 6. When there is aclearance between the front end face 2 a of the optical fiber 2 and thesecond inner wall 6 a and the clearance is filled with the adhesive 4,the adhesive 4 functions as a reflective-index matching agent.Accordingly, it is possible to suppress light loss.

Since the cured adhesive obstructs movement of the optical fiber 2 afterthe optical fiber 2 is adhered and fixed, it does not matter that theoptical fiber 2 is adhered and fixed in a state in which the front endface 2 a of the optical fiber 2 contacts the second inner wall 6 a or isclose to the second inner wall 6 a with a clearance therebetween. Thatis, it is preferable that the direction of the front end of the opticalfiber 2 protruding from the first inner wall 6 b to the recess 6 can bemaintained and unchanged between an adhesive filling process and anadhesive curing process.

In the present embodiment, a distance L between the first inner wall 6 band the second inner wall 6 a is less than or equal to four times theouter diameter D of the optical fiber 2. That is, the value of L/D is 4or less (L/D≦4).

When the distance L between the first inner wall 6 b and the secondinner wall 6 a in the recess 6A of the ferrule 1A is excessively greaterthan the outer diameter D of the optical fiber 2 as shown in FIG. 2, ashrinkage 4 a of the adhesive 4 occurs when the adhesive 4 is cured, andthe front end face 2 a of the optical fiber 2 moves and deviates from acentral axis C of the optical fiber 2 positioned by the positioningmechanism 7, as shown in FIG. 3. In this case, a deviation occurs in anoutput direction of light from the front end of the optical fiber 2 (oran input direction of light to the front end of the optical fiber 2),and making it difficult to match positions of optical fiber 2 when theoptical fiber 2 is optically connected to another optical part. Inparticular, when the ferrule includes a member (not shown) forconnection with a board or a module having the other optical partmounted thereon, the deviation of the output or input direction of theoptical fiber 2 makes it difficult to change and adjust the direction ofthe entire ferrule.

As shown in FIG. 3, the shrinkage 4 a of the adhesive 4 is larger in acentral portion of the recess 6A in the longitudinal direction of theoptical fiber 2 (a horizontal direction of the paper), and smaller atthe inner walls 6 a and 6 b at both sides of the recess that areopposite to each other in the longitudinal direction. Such a phenomenoncan be understood that the shrinkage 4 a is suppressed by interactionbetween the adhesive 4 and the inner walls 6 a and 6 b. However, whenL/D is great, the movement of the adhesive 4 occurs even in the vicinityof the second inner wall 6 a due to the shrinkage 4 a of the centralportion. Moreover, a length of the optical fiber 2 protruding as acantilever from the positioning mechanism 7 increases. Therefore, thefront end portion of the optical fiber 2 is bent with failure ofresistance against the movement of the adhesive 4. As a result, it isunderstood that the direction of the front end portion of the opticalfiber 2 deviates.

On the other hand, as shown in FIGS. 1A and 1B, when L/D is 4 or less,the length of the optical fiber protruding from the positioningmechanism 7 is small. Therefore, by the rigidity of the optical fiber 2itself, the movement of the front end portion of the optical fiber 2caused by the shrinkage of the adhesive 4 is suppressed to a negligiblelevel. As a result, the direction of the front end of the optical fiber2 cannot deviate.

The lower limit of L/D is not particularly limited, and it is preferablethat the distance L between the first inner wall 6 b and the secondinner wall 6 a is secured to the extent that the adhesive 4 is allowedto be applied into the recess 6. For example, when the outer diameter Dof the optical fiber 2 is 0.125 mm, it is preferable that L is about0.06 mm or more and L/D is 0.5 or more.

When the shrinkage of the adhesive 4 increases, a movement amount of thefront end portion of the optical fiber 2 increases. This tends toincrease the deviation of the direction of the front end of the opticalfiber 2. Therefore, it is preferable to use the adhesive 4 with a smallshrinkage ratio. For example, it is preferable to use adhesive with ashrinkage ratio of 3 to 5% rather than adhesive with a shrinkage ratioof 5 to 10%. When the adhesive applied into the recess 6 of the ferrule1 has a depth of Z before curing and a depth of Z−ΔZ after curing, theshrinkage ratio of the adhesive can be obtained using the followingequation:

(shrinkage ratio of adhesive)=(shrinkage amount ΔZ)/(filling depth Zbefore adhesive is cured)×100(%)

According to the ferrule 1 of the present embodiment, the deviation inthe output (or input) direction of each optical fiber 2 becomes small.Accordingly, the ferrule 1 of the present embodiment is particularlysuitable as a multi-core ferrule in which a plurality of optical fibers2 are adhered and fixed.

In the case of the multi-core ferrule, when connection loss exceeds anallowable range at one of a plurality of optical fibers adhered andfixed to the ferrule, the ferrule with optical fibers is treated as adefective product. Therefore, when distinctly manufacture a ferrule withoptical fibers in which connection loss of all the optical fibers is inthe allowable range, the effect of the present invention that reducesthe directional deviation of the front end of the optical fiber when aplurality of optical fibers are adhered and fixed to the ferrule is moreprominent.

The ferrule 1 of the present embodiment has advantageous effect aboutits miniaturization because of its simple structure. For example, thesize of the ferrule 1 is not particularly limited, but the ferrule 1,for example, may be 7 mm long or less and 7 mm wide or less.

(Modified Example of Ferrule)

Next, a ferrule 101 of a modified example will be described. The ferrule101 of the modified example is different from the above-describedferrule 1 in that the ferrule 101 includes a lens 108. Identicalreference numerals are used for the elements which are identical tothose of the first embodiment, and the explanations thereof are omittedor simplified here.

FIG. 14 is a perspective view showing the ferrule 101. FIG. 15 is across-sectional view partially showing the ferrule 101 into which theoptical fiber 2 is to be inserted.

The ferrule 101 is formed of a ferrule body 105. The ferrule body 105 isa single member made of a resin material. As a resin material used toform the ferrule body 105, polyetherimide, polycarbonate, cyclic olefincopolymer, cyclic olefin polymer, or other transparent polymers may beadopted. Part of the ferrule body 105 which serves as an optical pathfrom the optical fiber 2 to the lens 108 may be only formed of atransparent member.

As shown in FIG. 14, the ferrule 101 includes a front-end face(connection edge face) 118, a rear-end face 118, and a side surface 101c. The front-end face 118 is to be butt-jointed to a ferrule of theother optical connector (not shown in the figure). The rear-end face 119is located on the opposite side of the front-end face 118. The front-endface 118 is located close to the front end face 2 a of the optical fiber2. The side surface 101 c is located between the front-end face 118 andthe rear-end face 119 of the ferrule 101.

As shown in FIG. 15, the ferrule 101 includes a positioning mechanism 7which positions a center portion of the optical fiber 2. In thepositioning mechanism 7, the optical fiber 2 is located. The opticalfiber 2 is fixed to the positioning mechanism 7 by, for example, anadhesive.

A recess 106 is provided on the side surface 101 c of the ferrule 101.The recess 106 is opened on the side surface 101 c. The recess 106 iscommunicated with the positioning mechanism 7. The recess 106 is formedin a rectangular shape in a plan view. The recess 106 has a first innerwall 106 b for allowing a front end portion of the optical fiber 2positioned by the positioning mechanism 7 to protrude, and a secondinner wall 106 a opposite to the first inner wall 106 b. The secondinner wall 106 a is positioned between the optical fiber 2 and the lens108. The front end face 2 a of the optical fiber 2 is brought intocontact with the second inner wall 106 a.

A distance L between the first inner wall 106 b and the second innerwall 106 a is less than or equal to four times the outer diameter D ofthe optical fiber 2. That is, the value of L/D is 4 or less (L/D≦4).

As shown in FIG. 15, the recess 106 is filled with an adhesive(refractive index matching material) 4. As a result, it is possible toprevent the front-end position of the optical fiber 2 from beingdisplaced during use.

The ferrule 101 has inclined surfaces 125 a and 125 b, with an adhesiveapplication slot 106 d having an opening size increasing toward the sidesurface 101 c, between inner walls 106 a and 106 b of a recess 106 andthe side surface 101 c. Accordingly, even when a distance L between thefirst inner wall 106 b and the second inner wall 106 a is small, theadhesive application slot 106 d can have an increasing opening areaabove the recess 106. Accordingly, when the adhesive 4 is applied asdrops from above the recess 106, the adhesive 4 easily enters the recess106 through the adhesive application slot 106 d.

A recess 109 is provided on the front-end face 118 of the ferrule 101.The recess 109 is depressed with respect to the front-end face 118. Aplurality of lenses 108 are formed on the surface 109 a that facesforward of the recess 109. The lenses 108 are accommodated in the recess109 and do not protrude forward from the front-end face 118. The lenses108 are located on the extension lines P of the inserted optical fibers2. The lenses 108 are arranged to be optically aligned withcorresponding optical fiber insertion holes (optical alignment).

The plurality of lenses 108 are molded integrally in one body whichserves as part of the ferrule 101. The lenses 108 collimate lightemitted from the front ends of the optical fibers 2. The lense 108condenses, on the front end of the optical fiber 2, light emitted fromthe other ferrule that is butt-jointed to the ferrule 101. It ispreferable that the focal point of the lens 108 be located on the thesecond inner wall 106 a.

FIGS. 4 to 6 shows an example of a ferrule 11 that is suitable for anoptical connector used for optical connection with an optical element 17mounted on a photoelectric conversion module 16.

The ferrule 11 shown in FIG. 4 includes a ferrule body 20 comprising apositioning mechanism 22 for positioning an intermediate portion of anoptical fiber 12, and a recess 21. This recess 21 has a first inner wall21 b for allowing a front end portion of the optical fiber 12 positionedby the positioning mechanism 22 to protrude, and a second inner wall 6 aopposite to the first inner wall 21 b.

As shown in FIGS. 5A and 5B, in the ferrule body 20, a lower surface 20a is a bonding surface opposite to the photoelectric conversion module16, and the recess 21 is formed at an upper surface 20 b opposite to thelower surface 20 a. The optical fiber 12 protrudes from a first innerwall 21 b, and adhesive 14 is filled into the recess 21 and cured in astate in which the optical fiber 12 substantially contacts a secondinner wall 21 a to fix the optical fiber 12.

In the present embodiment, a plurality of optical fibers 12 arecollectively coated with one coating 13 to form a tape-shaped opticalfiber core wire (fiber ribbon). The tape-shaped optical fiber core wiremay be inserted into the ferrule 11 together with a boot 15, as shown inFIG. 4. A boot accommodating hole 23 is formed on a rear end surface 20d of the ferrule body 20, and when the optical fiber 12 is inserted intothe positioning mechanism 22, the boot 15 is accommodated in the bootaccommodating hole 23.

The boot 15 has a cross-sectional surface of a substantially rectangularcylindrical shape, and has a through hole 15 a into which the opticalfiber is inserted. The boot accommodating hole 23 has a greatercross-sectional area of an opening than the positioning mechanism 22.The boot accommodating hole 23 has substantially the same width andthickness as the boot 15. The boot 15 is engaged with the bootaccommodating hole 23 by the elastic force thereof. The boot 15 may besecurely fixed to the boot accommodating hole 23 by an adhesive (notshown).

When a plurality of optical fibers 12 are mounted to the ferrule 11, therecess 21 communicates with the positioning mechanism 22 for eachoptical fiber 12 and is formed over an entire arrangement range of theplurality of optical fibers 12 in an arrangement direction of theoptical fibers 12 (a vertical direction in FIG. 4). In this case, onlyif the adhesive 14 is applied into the single recess 21, all the opticalfibers 12 can be adhered and fixed.

The recess 21 has inner walls 21 a and 21 b, a bottom portion 21 c, andan adhesive application slot 21 d, like the recess 6 of theabove-described ferrule 1. Since the structure of the recess 21 and theadhesive 14, adhering and fixing of the optical fiber 12 in the recess21 or the like, may be the same as those of the recess 6 and theadhesive 4 of the above-described ferrule 1, a description thereof willbe omitted.

As shown in FIG. 6, the photoelectric conversion module 16 has anoptical element 17 mounted thereon or embedded therein. Examples of theoptical element 17 include a light emitting element such as asemiconductor laser (e.g., a laser diode; LD) or a light receivingelement such as a photo diode (PD). The photoelectric conversion module16 is provided on a circuit board (not shown) and has a function fordriving the light emitting element based on a control signal from adriving circuit on the circuit board, and a function of delivering anelectrical signal output from the light receiving element to aprocessing circuit on the circuit board.

The photoelectric conversion module 16 includes a holder member (notshown) for holding the ferrule 11 having the optical fiber 12 fixedthereto (a ferrule with an optical fiber 10). The structure of theholder member is not particularly limited thereto, but may be an armsupported by a spring, latch, pin engagement, magnet or the like. Whenthe ferrule with an optical fiber 10 is held on the photoelectricconversion module 16, the lower surface 20 a of the ferrule body 20 isopposite to the optical element 17. In this case, the optical fiber 12positioned by the positioning mechanism 22 is disposed in parallel withthe circuit board and so on. The positioning mechanism 22 may be inparallel with or inclined with respect to the lower surface 20 a of theferrule body 20.

The front face 20 c of the ferrule body 20 is located on an extendedline of an optical path 12 b to which the front end face 12 a of theoptical fiber 12 disposed in the recess 21 is directed. A reflectingportion 24 for changing optical paths 12 b and 17 a between the frontend of the optical fiber 12 and the optical element 17 is provided onthe front face 20 c. The reflecting portion 24 reflects, from its innersurface, light propagating in the ferrule body 20 based on a differencein reflective index between the ferrule body 20 and an external medium(e.g., air). A metal layer or a resin layer may be provided on the frontface 20 c to improve reflectance. It is preferable that the reflectingportion 24 has high reflectance.

The reflecting portion 24 may be, for example, a surface inclined withrespect to a longitudinal direction of the optical fiber 12 positionedby the positioning mechanism 22 and to a direction perpendicular to thelongitudinal direction. An inclination angle of the reflecting portion24 is not particularly limited, and when the optical path 12 b ofoptical fiber 12 is substantially perpendicular to the optical path 17 aof the optical element 17 as shown in FIG. 6, the inclination angle maybe about 45°.

In the embodiment shown in FIG. 6, the front face 20 c of the ferrulebody 20 is an inclined face formed close to the recess 21 from the lowersurface 20 a to the upper surface 20 b to be coincident with theinclination angle of reflecting portion 24. When a plurality of opticalfibers 12 are mounted to the ferrule 11, it is advantageous from amanufacturing viewpoint, e.g., a mold manufacturing cost, to make thereflecting portions 24 corresponding to the respective optical fibers 12coplanar at the front face 20 c. In the present embodiment, the frontface 20 c formed as the reflecting portion 24 is coplanar over an entirearrangement range of the plurality of optical fibers 12 in anarrangement direction of the optical fibers 12 (a vertical direction inFIG. 4).

When the optical element 17 is a light emitting element, the reflectingportion 24 reflects light incident from the lower surface 20 a towardthe front end face 12 a of the optical fiber 12. On the other hand, whenthe optical element 17 is a light receiving element, the reflectingportion 24 reflects light output from the front end face 12 a of theoptical fiber 12 toward the optical element 17 through the lower surface20 a. When the optical element 17 is a composite element having alight-emitting unit and a light-receiving unit, optical connection maybe performed through the reflecting portion 24 in a direction from theoptical element 17 to the front end of the optical fiber 12 and adirection from the front end of the optical fiber 12 to the opticalelement 17.

A ferrule with an optical fiber 10A shown in FIGS. 7A and 7B hasinclined surfaces 25 a and 25 b, with an adhesive application slot 21 dhaving an opening size increasing toward an upper surface 20 b, betweeninner walls 21 a and 21 b of a recess 21 and the upper surface 20 b.Accordingly, even when a distance L between the first inner wall 21 band the second inner wall 21 a is small, the adhesive application slot21 d can have an increasing opening area above the recess 21.Accordingly, when the adhesive 14 is applied as drops from above therecess 21, the adhesive 14 easily enters the recess 21 through theadhesive application slot 21 d. In the present embodiment, the openingsize was increased in the longitudinal direction of the optical fiber 12(a horizontal direction of the paper in FIG. 7A). When a smaller numberof optical fibers 12 are arranged (there may be one optical fiber, i.e.,the ferrule may be a single-core ferrule), the opening size may beincreased in a direction perpendicular to the longitudinal direction ofthe optical fiber 12 (a vertical direction of the paper in FIG. 7A) tofacilitate the application of the adhesive 14.

The inclined surfaces 25 a and 25 b may be provided at at least one ofthe first inner wall 21 b and the second inner wall 21 a, and may beprovided at both of the inner walls 21 a and 21 b, as shown. Aninclination angle of the inclined surfaces 25 a and 25 b is about 45° inthe shown example, but the angle is not particularly limited. Forexample, the angle may be 30 to 60°. When the inclined surface 25 aprovided in the second inner wall 21 a does not reach the front face 20c with the reflecting portion 24, a flat part of the upper surface 20 bis formed between the inclined surface 25 a and the front face 20 c,which is advantageous in terms of molding of the ferrule body 20.

An example of the structure in which the opening size of the adhesiveapplication slot 21 d is larger than the distance L between the firstinner wall 21 b and the second inner wall 21 a includes a structure inwhich the above-described inclined surfaces 25 a and 25 b are not onlyformed, but also the entire inner walls 21 a and 21 b are curved orinclined, and the size of the recess 21 is gradually increased towardthe upper surface in a tapered form. As long as the above-describedrequirement, L/D≦4, is satisfied, it does not matter that the recess 21has an opening larger than four times the outer diameter D of theoptical fiber 12, at a height portion above the positioning mechanism 22in which there is no optical fiber 12.

A ferrule with an optical fiber 10B shown in FIGS. 8A and 8B has afocusing lens 26 on a lower surface 20 a of a ferrule body 20. Thefocusing lens 26 is, for example, a convex lens. This focusing lens 26is disposed between a reflecting portion 24 and an optical element 17,and focuses light from the reflecting portion 24 toward the opticalelement 17, or vice versa (i.e., from the optical element 17 toward thereflecting portion 24) to suppress connection loss. An outer face of theferrule body 20 may be formed in a convex shape, such that the focusinglens 26 can be integral with the ferrule body 20. Further, a lensseparate from the ferrule body 20 may be fixed to the ferrule body 20.

A concave portion 26 a may be formed in the lower surface 20 a of theferrule body 20 and the focusing lens 26 may be formed in the concaveportion 26 a to prevent the focusing lens 26 from protruding from thelower surface 20 a of the ferrule body 20 downward. It is preferablethat when the depth of the concave portion 26 a is larger than aprotrusion size of the focusing lens 26, the focusing lens 26 isaccommodated inward from the lower surface 20 a of the ferrule body 20(in an upper direction of the paper in FIG. 8B).

When a plurality of optical fibers 12 are fixed to the ferrule body 20as shown in FIG. 8A, a focusing lens 26 is provided for each of theoptical fibers 12. In this case, the plurality of focusing lenses 26 arearranged in an arrangement direction of the optical fibers 12. Theconcave portion 26 a may be provided for each focusing lens 26, or maybe formed so that the plurality of focusing lenses 26 are disposed inone concave portion 26 a as illustrated in FIG. 8A. The concave portion26 a may be a groove portion that is formed in a rectangular shape onthe lower surface 20 a.

A ferrule with an optical fiber 10C shown in FIGS. 9A and 9B has areflecting portion 27 with a curved surface provided on a front face 20c of a ferrule body 20. The reflecting portion 27 may be, for example, arecessed reflecting surface and may be a spherical surface or anon-spherical surface. This reflecting portion 27 is located between afront end of the optical fiber 12 and an optical element 17, andfunctions as a concave mirror with respect to the front end of theoptical fiber 12 and the optical element 17.

Accordingly, it is possible to focus light between the optical fiber 12and the optical element 17 and suppress connection loss. That is, whenthe optical element 17 is a light emitting element, the reflectingportion 27 focuses, toward the front end of the optical fiber 12, lightemitted from the optical element 17 to the reflecting portion 27. On theother hand, when the optical element 17 is a light receiving element,the reflecting portion 27 focuses, toward the optical element 17, lightemitted from the front end of the optical fiber 12 to the reflectingportion 27.

A focal point of the reflecting portion 27 may be located on the frontend face 12 a of the optical fiber 12, on a light-emitting face of theoptical element 17, or on a light-receiving face of the optical element17, with a small deviation allowed.

The reflecting portion 27 reflects light propagating inside the ferrulebody 20 from its inner surface based on a difference in reflective indexbetween the ferrule body 20 and an external medium (e.g., air). Further,a metal layer or a resin layer may be provided on the front face 20 c toimprove reflectance. It is preferable that the reflecting portion 27 hashigh reflectance. The reflecting portion 27 may have a concave shape,when viewed from light reflected by the inner surface thereof. That is,the ferrule body 20 may be formed integrally with the reflecting portion27 so that the front face 20 c of the ferrule body 20 has a convexshape, when viewed from the outside. Further, a concave mirror which isseparate from the ferrule body 20 may be fixed to the ferrule body 20.

When a plurality of optical fibers 12 are fixed to the ferrule body 20as shown in FIG. 9A, the reflecting portion 27 is provided to eachoptical fiber 12 and the plurality of reflecting portions 27 arearranged in an arrangement direction of the optical fibers 12.

A positioning mechanism 22 may be an optical fiber hole 22 a entirelysurrounding the optical fiber 12, as shown in FIG. 10A. When a throughhole with a small diameter, such as the optical fiber hole 22 a, isformed in a integral mold, a pin-shaped mold is disposed in the positionof the optical fiber hole upon molding the ferrule body 20 to preventthe inflow of material, such that the optical fiber hole can be formedsimultaneously with molding of the ferrule body 20. Since this techniquecan easily form a high-precision optical fiber hole 22 a in comparisonwith post-processing using, for example, a drill, the technique isparticularly suitable for a multi-core ferrule 11 with a plurality ofoptical fiber holes 22 a.

The V-shaped groove 22 b shown in FIG. 10B, the U-shaped groove 22 cshown in FIG. 10C or the like may be employed as the positioningmechanism 22.

In this case, as shown in FIG. 11, a ferrule body 28 having an opticalfiber-accommodating groove such as the V-shaped groove 22 b or theU-shaped groove may be covered with a pressing lid 29 formed as aplate-shaped member, and the optical fibers 12 may be adhered and fixedbetween the ferrule body 28 and the pressing lid 29.

While the preferred embodiments of the present invention have beendescribed, the present invention is not limited to the above-describedembodiments and variations may be made to the present invention withoutdeparting from the scope of the present invention.

While in FIGS. 6 to 9B, the reflecting portion 24 or 27 of the ferrulebody 20 is formed on the front face 20 c that is an outer face of theferrule body 20, the present invention is not limited thereto. Thereflecting portion may be formed inside the ferrule body 20. Forexample, a concave portion having a cross-sectional surface of a V-shapemay be formed from the upper surface 20 b of the ferrule body betweenthe front face 20 c of the ferrule body 20 and the recess 21, and usedas the reflecting surface. Alternatively, a thin metal piece, as areflecting mirror, may be implanted in the ferrule body to form thereflecting portion.

EXAMPLES

Hereinafter, an example of the present invention will be described indetail. The present invention is not limited to the examples.

In this example, a multi-core (12-core) tape-shaped optical fiber corewire with a silica optical fiber having an outer diameter of 0.125 mmwas used as an optical fiber. The ferrule body 20 having the structurein which the front end portion of the optical fiber 12 is fixed in therecess 21 by the adhesive 14, and the directions of the optical paths 12b and 17 a are changed 90° by the reflecting portion 24 formed as a flatface on the front face of the ferrule body 20 to optically connect theoptical fiber 12 with the optical element 17, as shown in FIGS. 12A and12B, was used as a ferrule. An optical fiber hole having an innerdiameter of 0.127 mm was used as the positioning mechanism 22 of theferrule.

The distance L between the first inner wall 21 b and the second innerwall 21 a of the recess 21 in each sample was designed so that L/D was0.5, 1, 2, 3, 4, 5 and 6, and these seven types of samples weremanufactured, the number of the respective manufactured samples beingabout 30, as shown in Table 1. 12 optical fiber holes were formed in oneferrule to position and fix 12 optical fibers.

For each optical fiber, a beam angle α with respect to a referencedirection perpendicular to the lower surface 20 a as shown in FIG. 12Bwas measured. Here, the reference direction corresponds to an opticalaxial direction of the optical element 17 when the optical element 17 isoptically connected to the optical fiber. The beam angle α correspondsto a beam angle with respect to the optical axial direction of theoptical element 17. In this example, the beam angle α is obtained bymeasuring an angle when light output from the optical fiber 12 isreflected and output by the reflecting portion 24, as an angle deviatingfrom the reference direction. When the front end portion of the opticalfiber 12 is moved, for example, due to the shrinkage 14 a of theadhesive 14, the optical path 12 b deviates from a regular direction andthe beam angle α increases.

For about 30 ferrules with L/D=0.5, L/D=1, L/D=2, L/D=3, L/D=4, L/D=5,and L/D=6 and about 360 optical fibers, beam angles α were measured. Foreach L/D, a standard deviation of the beam angle α of each 12-coreoptical fiber was calculated and averaged to obtain a standard deviationof the beam angle α for each L/D. The result is shown in Table 1. InFIG. 13, the result of Table 1 is shown by a graph.

TABLE 1 Standard deviation (°) L/D of beam angle α 0.5 0.07 1 0.09 20.08 3 0.08 4 0.09 5 0.18 6 0.22

As shown in Table 1 and FIG. 13, when the distance L between the innerwalls 21 a and 21 b of the recess 21 is designed so that L/D≦4, thestandard deviation of the beam angle α was decreased. On the other hand,when L/D is 5 or more, the standard deviation of the beam angle α wasgreatly increased. It has been found from this result that when L/D≦4, aferrule with small connection loss can be manufactured with a higheryield.

What is claimed is:
 1. A ferrule for optically connecting an opticalfiber to an optical part, the ferrule comprising: a boot accommodatinghole which is configured to accommodate a boot attached to the opticalfiber and which is formed on a rear end surface of the ferrule; anoptical fiber hole which is configured to position an intermediateportion of the optical fiber having a predetermined outer diameter andwhich extends forward from a front end of the boot accommodating hole;and a recess configured for an adhesive to be disposed therein andcomprising a first inner wall from which a front end of the opticalfiber positioned by the optical fiber hole is protrudable, and a secondinner wall opposite to the first inner wall, wherein: the second innerwall is configured to be abutted by almost an entire area of a front endsurface of the optical fiber; a bottom of the recess is positioned lowerthan a lower edge of the front end of the optical fiber that protrudedfrom the first inner wall; the recess comprises an adhesive applicationslot with an opening larger than the distance between the first innerwall and the second inner wall, the first inner wall comprising a firstinclined surface, and the second inner wall comprising a second inclinedsurface which does not reach a front face of the ferrule; and a distancebetween the first inner wall and the second inner wall is more than orequal to half of the outer diameter of the optical fiber and less thanor equal to four times the outer diameter of the optical fiber.
 2. Theferrule according to claim 1, wherein the ferrule is formed of a resinthat is transparent to a wavelength of light transmitted through theoptical fiber.
 3. The ferrule according to claim 1, further comprising areflecting portion reflecting light on an optical path between the frontend of the optical fiber positioned by the optical fiber hole and theoptical part.
 4. An optical connector for optically connecting anoptical fiber to an optical part, the optical connector comprising: anoptical fiber; and a ferrule comprising: a boot accommodating hole whichis configured to accommodate a boot attached to the optical fiber andwhich is formed on a rear end surface of the ferrule; an optical fiberhole which is configured to position at least an intermediate portion ofthe optical fiber and which extends forward from a front end of the bootaccommodating hole; a recess comprising a first inner wall from which afront end of the optical fiber protrudes, and a second inner wallopposite to the first inner wall; and an adhesive disposed in the recessand a surrounding portion of the optical fiber protruding from the firstinner wall, wherein: a bottom of the recess is positioned lower than alower edge of the front end of the optical fiber that protruded from thefirst inner wall; the recess comprises an adhesive application slot withan opening larger than the distance between the first inner wall and thesecond inner wall, the first inner wall comprising a first inclinedsurface, and the second inner wall comprising a second inclined surfacewhich does not reach a front face of the ferrule; a distance between thefirst inner wall and the second inner wall is more than or equal to halfof the outer diameter of the optical fiber and less than or equal tofour times the outer diameter of the optical fiber; and substantially anentire area of a front end surface of the optical fiber abuts the secondinner wall.
 5. The ferrule according to claim 5, wherein a plurality ofthe optical fibers is fixed, and the reflecting portion comprises arecessed reflecting surface and is provided to each of the plurality ofthe optical fibers.
 6. The ferrule according to claim 7, wherein aplurality of the reflecting portions is arranged in an arrangementdirection of the plurality of the optical fibers.
 7. The ferruleaccording to claim 1, comprising a lens located on an extension line ofthe optical fiber.
 8. The optical connector according to claim 4,wherein the ferrule comprises a lens located on an extension line of theoptical fiber.